🔎 Search Terms
reachability never
🕗 Version & Regression Information
It's observed in all TS versions.
⏯ Playground Link
https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mAVAAjAUwG5oE4AoCUAXMgOJrrYCGUc2APOANZhwDuYANOltgHzIBvAFDJkUABbY2yAOTccMgNxCAvkKGhIsBCgC2lGGAKCRY7AE8To0eZhoANgBMU8vPmWiVyYIcr37lsLWyBAIAM5w9mgAdPZwAOa4Mj5gfgEy7qZqoqFgEVGxCUksUMjYaJQQ4pQARlEZympAA
💻 Code
function* never(): Generator<unknown,never> {
throw 'never';
}
function* main() {
try {
yield* never();
} finally {
console.log('finally');
}
console.log('not reachable');
}
🙁 Actual behavior
No error reported.
🙂 Expected behavior
There should be an error Unreachable code detected.(7027) at line 11 console.log('not reachable');.
Additional information about the issue
Reachability analysis is working for normal function: https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mABGApgNxQJwBQEoBcy6WiA3gFCKJQAWmcA7ogOSoabMDc5AvueaEiwEiALYBDGGDxlK1TAE9ZVKmyx5uVHomBTxAG31KKKxBAQBnOPpQA6fXADm2ZrrAGjzXJsR8q5sCsbeycXMDgoREwUcQgacQAjGy9uPiA
It's broken for Promise and we have another issue tracking that one: #34955
Generator functions are being used as coroutine in libraries like co.js, Effect.js, redux-saga, Effection, and more. It's common to write a coroutine operator that suspend the thread forever, thus taking function never(): Generator<Instruction, never> signature. It would benefit users if the TypeScript control analysis can infer unreachability after yield* never().
🔎 Search Terms
reachability never
🕗 Version & Regression Information
It's observed in all TS versions.
⏯ Playground Link
https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mAVAAjAUwG5oE4AoCUAXMgOJrrYCGUc2APOANZhwDuYANOltgHzIBvAFDJkUABbY2yAOTccMgNxCAvkKGhIsBCgC2lGGAKCRY7AE8To0eZhoANgBMU8vPmWiVyYIcr37lsLWyBAIAM5w9mgAdPZwAOa4Mj5gfgEy7qZqoqFgEVGxCUksUMjYaJQQ4pQARlEZympAA
💻 Code
🙁 Actual behavior
No error reported.
🙂 Expected behavior
There should be an error
Unreachable code detected.(7027)at line 11console.log('not reachable');.Additional information about the issue
Reachability analysis is working for normal function: https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mABGApgNxQJwBQEoBcy6WiA3gFCKJQAWmcA7ogOSoabMDc5AvueaEiwEiALYBDGGDxlK1TAE9ZVKmyx5uVHomBTxAG31KKKxBAQBnOPpQA6fXADm2ZrrAGjzXJsR8q5sCsbeycXMDgoREwUcQgacQAjGy9uPiA
It's broken for Promise and we have another issue tracking that one: #34955
Generator functions are being used as coroutine in libraries like co.js, Effect.js, redux-saga, Effection, and more. It's common to write a coroutine operator that suspend the thread forever, thus taking
function never(): Generator<Instruction, never>signature. It would benefit users if the TypeScript control analysis can infer unreachability afteryield* never().